The present invention relates to a method for detecting data recorded from a signal reproduced in a data storing unit and a device therefor, and more particularly, to a method for detecting data for recovering clock by limiting a sampling clock recovering process to operate only at an edge of a signal waveform in order to effectively detect the reproduced signal in case the recorded data is coded to a run length limited code whose runlength constraints are not less than one, and a device therefore
Research and development for effectively using massive information in the modern information conscious society has been rapidly advancing. As a result, remarkable developments have been achieved in various fields. Also, as societal demand to use information increases, delievering large quantities of information and reducing time for processing information, and increaing quantity of data recorded in a storing unit of a given capacity (recording density) become the biggest object in the storing field unit. There are methods for improving physical characteristics of a storage disk or precision degree of the data storing unit and for reducing data detecting errors using a signal processing technique, which can be regarded as efforts to maximize a speed and a capacity of such a data storing unit.
The data recorded in such a storing unit is the data encoded to the RLL code. This is an encoding method for preventing data symbols to be recorded from being continuously connected, in order to control timing of data sampling clock and to detect a signal. Namely, this is a runlength (d, k) code which limits the number of "0s" which continue between "1" and "l" into d in the minimum and k in the maximum. The former is for facilitating the signal detection and the latter is for timing of the data in recovering the reproduced signal. Since the characteristics of the reproduced signal are different according to the position on the disk, it is necessary to appropriately change a signal detecting method or an equalizer according to the characteristics of the signal for precise signal detection. Also, frequency and phase of the clock should be continuously adjusted so that the sampling is performed in an accurate position of a pulse during a procedure of sampling an analog signal to a symbol signal.
While, in case of an optical magnetic disk storing unit, it is possible to record the data in high density when the data is coded to the RLL code whose minimum runlength d is not less than one, considering the characteristics of a laser and a disk medium for recording the data. In a magnetic storing unit such as a hard disk driver, since it is hard to detect the data due to a nonlinear characteristic of the signal as the recording density increases, the data may be coded to the RLL code whose runlength d is not less than one in order to reduce the nonlinearity of the signal.
Generally, a channel should be modeled similarly to a real channel during recording and reproducing with respect to a storing unit. Such a channel characteristic of the unit can be expressed as (1+D).sup.n or (1-D)(1+D).sup.n, (here, n=1, 2, . . . ), according to a recording density in order to reflect the channel characteristic of the storing unit. Here, D denotes a time delay. Since interference between the recorded signals increases as the recording is performed in high density in the storing unit, the channel should be modeled with a larger n value to be expressed nearer to the real channel characteristic.
There are a decision feedback equalizer (DFE) method and a partial response maximum likelihood (PRML) method, etc, in recent data detecting methods. Among them, the DFE method is the method for changing an input signal to have only the present data value by equalizing it to a target response satisfying d.sub.k =a.sub.k and for detecting data with a normal threshold value detector. In the DFE method, it is easy to detect the data since the data is detected with the threshold detector and to control the sampling clock since the data is detected to every clock. However, in case signal interference is high, detecting performance is deteriorated since noise of a high frequency is amplified in the process of equalizing the input signal to meet d.sub.k =a.sub.k. Meanwhile, in the PRML method, the data is detected with a Viterbi decoder by changing the input signal into a target response satisfying d.sub.k =a.sub.k +a.sub.k-1 or d.sub.k =a.sub.k -a.sub.k-2 after generating inter-symbol interference (ISI) controlled between the present data and the previous data by preceding the input signal. In the recording density which has the signal interference in which the channel characteristic approximately meets n=1, it is possible to excellently detecting the data using the PRML method, however, it is hard to control the sampling clock since the data is not detected every clock.
To restore the data recorded on the storing unit, the bit clock should be restored from a reproduce signal. Such a restoration of the bit clock is for generating the clock synchronized with the bit clock and sampling it and for continuously obtaining a sample of a desired accurate value by tracking the change of the bit clock frequency of the reproduced signal. In general bit clock recovering methods, there are a method for directly extracting the bit clock by passing the reproduced signal over a narrow-band band pass filter and sampling the reproduced signal using the bit clock and a method for obtaining a sampling phase error from the sampling value obtained by sampling the reproduced signal and gradually adjusting the frequency of the sampling clock by removing the sampling phase error.
The latter method is widely used in processing the reproduced signal of the storing unit. In the latter method, the phase error of the sampling clock is detected, the sampling error is adjusted again according to the error, and a series of sampling clock recovering processes are performed to all the data patterns. Recovering the clock by sampling it every time in such a method is inefficient since, when continuous data rows of the same value are repeated, continuous sampling clock restorations are performed in the data which does not have timing information.